/* Check that |bst_t_first()| and |bst_t_next()| work properly. */
struct bst_traverser trav;
size_t i;
int prev = -1;
int *item;

for (i = 0, item = bst_t_first (&trav, tree); i < 2 * n && item != NULL;
     i++, item = bst_t_next (&trav))
  {
    if (*item <= prev)
      {
        printf (" Tree out of order: %d follows %d in traversal\n",
                *item, prev);
        okay = 0;
      }

    prev = *item;
  }

if (i != n)
  {
    printf (" Tree should have %lu items, but has %lu in traversal\n",
            (unsigned long) n, (unsigned long) i);
    okay = 0;
  }